I should update people on this as I have made progress today. I found two broken tracks from the 8742 peripheral controller to the ASICs. One of the ASICs sends a RESET to the 286. When I repaired that track suddenly the protected mode test started to pass. Now I have other errors which are almost certainly other bad tracks, although these errors are more intermittent so it could be a track that is partially damaged.
Regards Rob > -----Original Message----- > From: Rob Jarratt <robert.jarr...@ntlworld.com> > Sent: 06 March 2021 23:30 > To: 'Richard Pope' <mechani...@charter.net>; r...@jarratt.me.uk; 'General > Discussion: On-Topic and Off-Topic Posts' <cctalk@classiccmp.org> > Subject: RE: 80286 Protected Mode Test > > > > -----Original Message----- > > From: Richard Pope <mechani...@charter.net> > > Sent: 06 March 2021 23:20 > > To: r...@jarratt.me.uk; Rob Jarratt <robert.jarr...@ntlworld.com>; > > General > > Discussion: On-Topic and Off-Topic Posts <cctalk@classiccmp.org> > > Subject: Re: 80286 Protected Mode Test > > > > Rob, > > There is probably hidden damage to the motherboard. The acid will > follow > > the traces inside the board and consume them. There is no way to stop > > this kind of damage. Sorry for the bad news. > > I should have said that I have found a few bad tracks and I have fixed them > by adding wires. Previously it would not even POST, but it does now. The > CPU is physically distant from the battery damage. I am trying to understand > if this particular test could fail due to external factors or not so that I can then > investigate if there are other tracks I need to fix. > > Incidentally, my repair wires are done very badly, are there any tips on how > to do this well? I have ordered some wire wrap wire because I believe that is > what I should be using, but I haven't got the wire yet. > > Thanks > > Rob > > > GOD Bless and Thanks, > > rich! > > > > On 3/6/2021 4:59 PM, Rob Jarratt via cctalk wrote: > > > I have a DECstation 220 (Olivetti M250E) which is failing POST on a > > > "simple test of the 80286 protected mode". It says in a service > > > manual I have that for this test the CPU is set in the protected > > > mode, the machine status word is checked to see whether it indicates > > > the protected mode and then exits protected mode. This test seems to > > > be failing. Is there any possible explanation for this other than a > > > failed 80286 CPU? Could there be any external reason? This board > > > suffered some battery leak damage. Clearly the > > > 80286 is working well enough to execute this diagnostic and send > > > some text to the screen, so it basically works. > > > > > > > > > > > > Thanks > > > > > > > > > > > > Rob > > > > > >